In recent years, tactile sense presenting devices have been proposed as examples of vibrating devices which each feedback a sense of touch by transmitting vibrations when a user touches a key on a touch panel keyboard, and makes the user feel that the user has “pushed” a key.
For example, Patent Literature 1 discloses a structure which holds both ends of a piezoelectric bimorph element made of piezoelectric ceramics or the like by using low elastic bodies, and connects a vibration member to a center of the piezoelectric bimorph element. The structure according to Patent Literature 1 transmits vibrations to a user via the connected vibration member by inputting an alternating-current signal to the piezoelectric bimorph element to cause vibrations.
However, there is a problem that piezoelectric ceramics are likely to be cracked. Meanwhile, a member which is not likely to be cracked such as a piezoelectric film has low capability to transmit vibrations, and is difficult to use for a tactile sense presenting device.
Hence, for example, a structure which connects an end of a diaphragm of a thin flat shape to a piezoelectric film and applies a stress to the diaphragm may be adopted. In this case, the diaphragm vibrates in a direction orthogonal to a principal surface when the piezoelectric film stretches or contracts. A stress is applied to the diaphragm and, consequently, can be efficiently vibrated in response to the stretching or the contraction of the piezoelectric film. Further, by adjusting a frequency at which the piezoelectric film stretches or contracts, to a resonant frequency of the entire structure including the diaphragm and the film, it is possible to more efficiently cause vibrations.
Furthermore, for example, a structure which connects a piezoelectric film to a frame body composed of a member of a prism shape may be also adopted. In this case, prism members facing each other are connected by the piezoelectric film, and the piezoelectric film is disposed in an opening of the frame body. In this case, the piezoelectric film is disposed directly below a touch panel or the like, so that, when a user pushes the touch panel, the touch panel touches the piezoelectric film, and vibrations of the piezoelectric film are directly transmitted to the user. Consequently, it is possible to efficiently transmit the vibrations.
Patent Document 1: Japanese Patent Application Laid-Open No. 2005-303937